In conventional jig saws, the saw blade is usually moved back and forth along its longitudinal axis by means of a working rod. In conventional orbiting saws, a tilting motion is imposed on the saw blade during the working stroke to increase the cutting performance and, as a consequence, the saw teeth, particularly those near the tip of the saw blade, penetrate more deeply into the material to be sawed due to their slanted orientation.
These arrangements have certain additional disadvantages and drawbacks. For example, in conventional jig saws with a linear-motion saw blade, the backs of the cutting teeth are pressed into the material being sawed each time the blade makes its return stroke. Consequently, the saw blade can quickly dull, especially, if during the return stroke, the backs of the sensitive saw teeth are hammered against the cut edge of a hard material, such as metal. Furthermore, a great deal of force is expended and the operation of the saw runs are very irregular.
Conventional orbiting saws suffer additional disadvantages. For example, the orbiting saw blade is not guided perpendicularly to the cutting edge at all times. Instead, the saw blade is forced into a slanted position before each working stroke, thus impairing the accuracy of the cut.
In addition to linear-motion and orbiting jig saws, there also are jig saws that are driven by means of a cam via a parallelogram of rods. One such cam driven jig saw is demonstrated by the West German Patent No. 2,334,911 (FIGS. 5-7 in particular). Even in this type design where the saw blade is lifted off the cutting edge during the return stroke, a considerable amount of backward motion (backstroke) is caused during the return stroke. This is especially so when the rods of the parallelogram are short. Conversely, during the working stroke the amount of forward movement (forestroke) is large, which leads to heavy wear on the saw blade and can even lead to an overload on the drive. A large forestroke and backstroke impairs not only the cutting performance, but the ability to negotiate curves which precludes the cutting of smaller radii. Although this problem can be solved by increasing the length of the two parallel longitudinal side arms of the parallelogram of rods, this produces an undesirable increase in the overall dimensions of the saw, impairing the use as a machine-driven hand tool. In addition, a small working stroke results in a poor cutting performance.